Today, hot air blowers are used for a variety of applications including direct heating of part surfaces, incineration of gas particulates, and heating enclosed chambers. More particularly, hot air blowers can be used for refractory curing, plastics sealing, cleaning diesel exhaust, and retrofitting gas fired ovens and furnaces.
Such blowers typically comprise a blower fan, an electric heating element, and a housing for the heating element. The blower fan forces air into the housing through an inlet at one end of the blower. The air is then heated by convection and radiation as it passes near the heating element and is provided at the outlet at the opposite end of the blower.
Blowers designed with metallic heating elements have until now generated air temperatures up to 1,472.degree. F. (800.degree. C.). If a blower is made with molybdenum disilicide heating elements it is anticipated that such a blower can heat air higher than 1,832.degree. F. (1,000.degree. C.). While technical advances have allowed blowers to produce higher temperatures, there is a continual quest to produce even higher temperatures so that the range of applications of such blowers can be expanded. Furthermore, it is desirable to construct a blower having a maximum percentage of energy transfer efficiency, i.e. that transfers the maximum amount of electrical energy to heat energy thereby reducing the cost to operate the blower. In addition to limitations in temperature output and energy efficiency, current blowers suffer from other limitations as well. For example, it has been found that blowers with metallic heating elements are limited in their maximum temperature output because, in part, the heating element will crack if it becomes too hot relative to the air that passes near it.
Accordingly, it is desirable to construct a hot air blower that can produce higher temperatures than current hot air blowers. Furthermore, it is desirable to produce a hot air blower that has a higher energy efficiency than current blowers. Moreover, it is desirable to produce a hot air blower that does not cause the metallic heating element used within it to crack when the element reaches a certain temperature relative to the air passing near it.
Several advances have been made in the field of porous ceramic materials. For example, U.S. Pat. No. 5,279,737 (the '737 patent) and U.S. Pat. No. 5,558,760 (the '760 patent) disclose the use of porous ceramic materials as regenerative filters to clean exhaust emitted from engine-run vehicles such as buses. These references disclose methods for the production of such materials, which methods will be described in greater detail below. In addition, the '760 patent discloses the manufacture of a porous body that is conductive such that it can simultaneously act as a heating element as well as a filter, thereby eliminating the need for a heating element in the regenerative filter and decreasing the amount of heat lost due to radiation. While the references disclose the use of porous ceramic materials as regenerative filters, neither of these references disclose or suggest the use of a pair of such porous ceramic materials within a hot air blower. Nor do these references disclose or suggest the use of such materials for creating an air gap within a hot air blower, thereby increasing the temperature of the output air as well as the blower efficiency.